Wireless RF receivers are used in a wide variety of applications such as smart metering, remote control, home security and alarm, telemetry, garage and gate openers, remote keyless entry, and the like. As used herein, a “radio frequency” signal means an electrical signal conveying useful information and having a frequency from about 3 kilohertz (kHz) to thousands of gigahertz (GHz), regardless of the medium through which such signal is conveyed. Thus an RF signal may be transmitted through air, free space, coaxial cable, fiber optic cable, etc. One common type of RF receiver is a frequency-shift keying (FSK) receiver that is compatible with the industrial, scientific and medical (ISM) radio bands in the 119 to 1050 megahertz (MHz) range. ISM radio bands are portions of the radio spectrum reserved internationally for the use of RF energy for industrial, scientific and medical purposes other than communication.
Certain wireless communication standards define a preamble for a wireless packet which is basically a leading packet a receiver detects, and uses to settle its control loops. These control loops include the Automatic Gain Control (AGC), Automatic Frequency Compensation (AFC), and Bit Clock Recovery (BCR). After the receiver detects the end of the preamble, the receiver is prepared to receive a full packet of payload data. While many standards define a relatively long preamble pattern length (about 32 preamble bits in an alternating . . . 1010 . . . pattern) to provide enough time for these loops to settle, the N-mode of the wireless version of the Meter-Bus (M-Bus) standard, no. EN 13757-4, defines a relatively short preamble (about 16 bits in an alternating . . . 1010 . . . pattern). Although the shorter preamble provides an opportunity for the receiver to work faster and to take advantage of corresponding power savings, the shorter preamble also increases the burden on the receiver to reliably detect the signal arrival of the preamble, and to settle its control loops in time.
In general, known receivers need to settle the AFC before they can reliably detect the preamble. If the AFC tracks noise that is included in the RF signal, and wanders in response to the noise, the receiver could struggle to detect the preamble signal, and could miss the preamble and a subsequent data packet.
The use of the same reference symbols in different drawings indicates similar or identical items.